NOJIRA Allow empty URL
NOJIRA Fix broken save buttons
PROV-819 Source level access control implementation:

1. Added support for default source
2. Source drop-down in UI now restricted to allowed sources
3. Source restrictions bypassed for administrators
4. Begun consolidation of hierarchy code that needs source filtering
5. Removed findByLabel code; replaced with BaseMode::find()
6. Fixed various source ACL configuration issues